In general, an electronic device, such as a solar cell, an organic light emitting device, or an organic transistor, includes two electrodes and an organic compound layer interposed therebetween. For example, a solar cell generates electricity using electrons and holes separated from exitons that are generated in an organic compound layer by solar energy. An organic light emitting device converts a current into visible light by injecting electrons and holes from two electrodes into an organic compound layer. An organic transistor transports holes or electrons generated in an organic compound layer between a source electrode and a drain electrode by applying a voltage to a gate electrode. The electronic device may further include an electron/hole injection layer, an electron/hole extraction layer, or an electron/hole transport layer.
However, since the interfaces between the organic compound layer and the electrodes each containing a metal, a metal oxide, or a conductive polymer are unstable, heat from the outside, heat generated inside, or an electric field applied to the electronic device may have a bad effect on performance of the electronic device. Further, due to a conductive energy level difference between the organic compound layer and the electron/hole injection layer, the electron/hole extraction layer, or the electron/hole transport layer, a driving voltage for driving the electronic device may increase. Therefore, it is important not only to minimize the energy barrier for hole/electron injection to the electrodes and hole/electron extraction from the electrodes, but also to stabilize the interfaces between the organic compound layer and the electrodes and the interfaces between the organic compound and the electron/hole injection layer, the electron/hole extraction layer, and the electron/hole transport layer.
Electronic devices capable of adjusting the energy level differences between the electrodes and the organic compound layer interposed therebetween have been developed. In case of an organic light emitting device, in order to smoothly inject holes, an anode is adjusted to have a Fermi energy level similar to an HOMO (highest occupied molecular orbital) energy level of a hole injection layer or a material having an HOMO energy level similar to a Fermi energy level of an anode is selected as a material for a hole injection layer. However, since the hole injection layer should be selected in view of an HOMO energy level of a hole transport layer or an emitting layer close to the hole injection layer as well as in view of the Fermi energy level of the anode, there is a limitation to select a material for the hole injection layer.
For this reason, in general, a method of adjusting a Fermi energy level of an anode is used to manufacture an organic light emitting device. However, in such a method, a material for the anode is limited. In an organic transistor, gold or precious metals are used as materials of a source electrode and a drain electrode. However, precious metals, such as gold, are very expensive and are not easily processed compared with other metals. Therefore, the manufacturing process of the organic transistor is complicated and thus it is difficult to commercially use the organic transistor.